A turbomachine according to the prior art, which is designed as a radial turbine, is shown in FIG. 1 of the drawings herein. FIG. 1 is a section view of a portion of a conventional steam turbine in the form of a radial turbine which is designed for a steam flow below sonic velocity (subsonic flow). In a radial turbine, the corresponding operating medium flows in the radial direction with regard to a rotational axis of a rotor wheel and impinges upon the blades at the periphery of this rotor wheel. In the case of axial turbines, however, the operating medium flows in the axial direction with regard to a rotational axis of the rotor wheel. In the case of the turbine which is shown in FIG. 1, blade leading edges and blade trailing edges are formed, extending from the radial direction into the axial direction at an angle of 90°.
The turbomachine of FIG. 1, which is designed as a radial turbine, has an essentially fixed turbine housing 110, in which a turbine wheel 120 (rotor wheel) is arranged. The rotor wheel 120 comprises a multiplicity of (co-rotating) blades, wherein in FIG. 1 one blade 121 is shown as being representative. A gaseous operating medium, for example exhaust gas from an internal combustion engine, flows through an inlet passage or through a nozzle passage 100 of the turbine housing 110 according to a direction arrow 151 and drives the rotor wheel 120. To this end, the flowing operating medium is first accelerated in the nozzle passage 100 and deflected along a blade 121. The edges of the blade are oriented on one side in the region of an operating medium inlet parallel to the rotational axis of the rotor wheel 120 and at an operating medium outlet point 153 in the radial direction. The operating medium is guided in this case along its entire flow path in the rotor wheel between blades 121.
The rotor wheel 120 of the flow device (turbine) according to FIG. 1 is basically designed similar to the rotor wheel of a compressor, in which the operating medium which is driven through the blades flows in a direction which is oriented oppositely to the view according to FIG. 1. The flow in an operating state as a compressor can correspondingly be deflected inside the blades of the rotor wheel from the inside outwards in such a way that, after discharging from the blade passages at the operating medium outlet, the flow travels axially in relation to the rotor wheel. This type of construction of blade wheels or blading is well suited to operating medium or steam velocities below sonic velocity.
In the case of radial turbines according to the prior art, with rotor wheels in which the flow is deflected by 90° along its blading, difficulties arise if steam flows reach their sonic velocity.
A particular problem is that radial turbines for supersonic flows, with parallel blades which are oriented axially to the shaft, lead to vortex formation and consequently lose effectiveness.